The importance of PGE, particularly PGE.sub.2, in vivo is widely recognized. Analyses of the physiological and pharmacological action of PGE.sub.2 and action sites have suggested that there exist at least three types of PGE receptors, EP.sub.1, EP.sub.2 and EP.sub.3 and they are thought to be different in their signal transduction. These subtypes are presumed coupled to stimulation of phospholipase C, and stimulation and inhibition of adenylate cyclase, respectively. (R. A. Coleman, I. Kennedy, P. P. A. Humphrey, K. Bunce and P. Lumley, Comprehensive Medicinal Chemistry, ed. C. Hansch, P. G. Sammes and J. B. Taylor, Vol. 3, pp. 643-714, Pergamon Press, 1990 and Annu. Rev. Pharm. Tox. 10, 213-239 (1989)). Among PGE receptor subtypes, the EP.sub.2 receptor has been suggested to be involved in relaxation in trachea (Br. J. Pharmacol. 87, 45 (1986)) and ileum circular muscle (Br. J. Pharmacol. 105, 271-278 (1992)), vasodilatation in various blood vessels, and stimulation of sodium and water reabsorption in kidney tubulus (J. Clin. Invest. 47, 1154-1161 (1968) and J. Biol. Chem. 263, 6155-6160 (1988)). One of the most important functions of PGE.sub.2 through EP.sub.2 receptor has been proposed to be negative regulation of immune system (Am. Rev. Respir. Dis. 135, 72-77 (1987)) and inflammation, and the EP.sub.3 receptor has been suggested to be involved in such PGE.sub.2 actions as inhibition of gastric acid secretion (Chen et al., 1988. Gastroenterology 94, 1121-1129), modulation of neurotransmitter release (Hedqvist et al., 1972. Neuropharmacology 11, 177-187; Ohia and Jumblatt, 1990. J. Pharmacol. Exp. Ther. 255, 11-16), inhibition of lipolysis in adipose tissue (Richelsen et al., 1984. J. Lipid Res. 26, 127-134), and inhibition of sodium and water reabsorption in kidney tubulus (Garcia-Perez et al., 1984. J. Clin. Invest. 74, 68-74). However, no PGE.sub.2 receptor genes have been successfully cloned; their distribution, structure and function remain to be investigated. There has been urgent demand for their elucidation for the purpose of clarifying PGE-associated, particularly PGE.sub.2 -associated diseases, and for developing effective pharmaceuticals for such diseases.